This is a LWRC Brake known as the Ultra Static Brake chambered in 556NATO, model 200-0141A02.
LWRCI's new Ultra-Brake muzzle brake is the same great muzzle device featured on factory REPR MKII rifles. With four generous exhaust ports this brake helps balance and mitigate recoil keeping you on target.
Features:
1/2X28 thread pitch
